Conventionally, there has been used a throw away type cutting tool structured such that a cutting insert having a cutting edge is installed to a holder.
As the cutting insert used in the cutting tool mentioned above, for example, in patent document 1, there is disclosed a cutting insert provided with a cutting edge which is positioned at an intersection of an upper surface and a side surface, and a groove portion which is provided on the side surface in such a manner as to divide the cutting edge. Divided cutting edges divided by the groove portion contribute to a reduction of a cutting resistance.
On the other hand, in the case of using the cutting insert having the divided cutting edges as mentioned above, since an uncut part is generated in a portion corresponding to the groove portion, in the workpiece, it is necessary to install a cutting insert having a different arrangement of the groove portion into the holder. Specifically, two kinds of cutting inserts are attached to the holder in such a manner that located at a position on a rotational locus of the groove portion of one cutting insert installed to the holder is a cutting edge of the other cutting insert.
However, in the cutting tool to which these cutting inserts are attached, a great load is applied to the cutting edge portion of the other cutting insert corresponding to the groove portion of one cutting insert. Therefore, the cutting edge portion tends to be chipped.